The calibrating cage on a Z-bar type body forming machine is a device which confines the shell formed by a rolled body blank just prior to and during the seam welding process. This confinement is provided by structurally restraining the rolled can body to a diameter not exceeding the desired finished can outside diameter. Ideally, the restraint system should have no circumferential gaps in which the body blank metal can buckle or otherwise deform thus defeating the desired diameter control.
A calibrating cage heretofore used was a sleeve construction wherein a large portion of the body blank was restrained by the almost cylindrical surface of the sleeve. This construction evolved from test fixture developmental trials devoted primarily to the body control and welding of low basis weight -- 55# plate. Other welding cage configurations were evaluated such as a roller cage, air bearing, and ball bearing construction. The latter two developments were associated with a sleeve type cage geometry. The roller type cage type requires continuous adjustments of the can body embracing rollers which is extremely difficult in the environment in which the cage is located and is subject to visual observation and thus is inaccurate.
Competing welding processes utilizes a roller type cage for body control. The roller cage type, although continuously being modified by industrial manufacturers, has generally been successful for high basis weight plate exceeding 70#. Very little information, no less commercial operation, is available regarding the ability to control 55# plate bodies with a roller cage.
The continuous cylindrical sleeve type cage was previously employed in a commercial Z-bar operation.
The next stage in the Z-bar development process was to provide a commercial machine for the production of 211 .times. 713 aerosol cans. This required the utilization of 75# and 80# plate. One of the first observations made when welding the higher basis weight plate was that an increased frictional drag was imposed on the body blank when traversing the sleeve cage. The second and most serious observation was the formation of a defect at the leading edge of the can body. The most prevalent form of the defect was the formation of a thinned metal region just adjacent to the cut edge overlap at the lead edge. Sometimes the defect appeared as unbond despite adequate weld structure temperature or simply appeared as a single longitudinal crack in the welded overlap. No matter what appearance the lead edge defect had; the results were either cracks or effective cracks after flanging. The supposition was made that no matter what appearance the defect had, the cause was the same.